The present invention relates to a new and improved construction of diaphragm press for agricultural products, such as grapes, fruits and other fruit-like products. The diaphragm press of the invention is of the type which comprises a press container which is mounted and driven so as to be rotatable about its horizontal lengthwise axis.
For a long time diaphragm presses have been generally used for pressing-out or squeezing liquid-containing materials or substances. Owing to their simple design and, with respect to the material to be pressed the gentle and protective mode of operation of these diaphragm presses, preferred fields of application thereof have been the pressing-out of laundry and organic materials, such as brewery mash, grapes, fruits and other fruit-like products. The press container, if desired, may be constructed so as to serve at the same time as a rotatable washing container.
In U.S. Pat. No. 2,538,403, granted Jan. 16, 1951, there is disclosed a diaphragm press which is intended to be used especially, but not exclusively, for brewery mash. The press container possesses a substantially longitudinal cylindrical shape and contains a substantially bag-shaped diaphragm. Approximately at the longitudinal central region of the upright container this bag-shaped diaphragm is attached to the jacket or shell of the container and is located in a plane which is perpendicular with respect to the container axis. The diaphragm possesses the advantage that during the extraction or pressing operation it simply needs to be inverted or placed inside out, and thus is not exposed to unfavorable stresses during the pressing process, such as excessive stretching, even when used with unusually large press containers. However, the direct use of this prior art press in winemaking or similar fields is hindered by virtue of the only pivotable mounting of the press container. This is so because winemaking presses are in any case, i.e. even if constructed as piston presses, provided with a rotating or revolving press container, so that between the pressing cycles the mash is loosened and rearranged, and thus, the efficiency of the juice extraction or dejuicing is increased. In this regard, it should be clearly understood that the term "winemaking press" as used herein is employed in the broadest sense and is not intended to be limited to a particular material to be pressed.
The large-scale or increased employment of diaphragm presses in winemaking started about three decades ago. The construction of these diaphragm presses, however, initially was governed by certain aspects which were not necessarily fulfilled by conventional diaphragm presses. In particular, as disclosed in German Pat. No. 1,001,589, efforts were made to enlarge the surface of the diaphragm in proportion to the amount of material to be pressed. Therefore, the diaphragm was given the shape of a hose or tube which was secured to the face ends or sides of the elongated press container which rotated about its horizontal lengthwise axis. This hose-shaped or tubular diaphram had a relatively large diameter compared to the diameter of the press container and together with the jacket or shell of the container formed a correspondingly narrow, substantially ring-shaped press compartment or chamber. It was considered advantageous not only that the diaphragm surface was correspondingly enlarged, but also that the material to be pressed was distributed around the diaphragm in the form of a rather thin layer. The underlying idea was that there thus could be achieved shorter outflow or outlet paths for the juice, and hence, the yield in juice per pressing cycle could be increased. Furthermore, it was assumed that the expansion of the hose or tube would not entail only a radial pressing of the mash, rather that such mash also was displaced in the direction of the periphery of the press container, and thus, there were continually opened up new outflow or outlet paths for the juice.
Presses of this type have proved to be useful. However, it has been found that when rotating the container between the pressing cycles for loosening or slackening the material to be pressed, the diaphragm is thus exposed to mechanical stress and consequently has to be frequently exchanged. It has further been found that the possible increase of the yield in juice by means of the ring-shaped distribution of the material to be pressed around the hose-shaped diaphragm is extensively annihilated by the fact that even with an unloaded diaphragm the press chamber or compartment only occupies an annular fraction of the entire space of the press container and the constantly present pressure chamber, surrounded by the diaphragm, markedly impairs the receiving capacity of the press container. Even if the juice flowed out faster, the press container had to be more frequently emptied and refilled for processing the same amount of pressible material. With any size of the press container this procedure costs more time than could be gained by means of the shorter outflow or outlet paths for the juice.
In order to eliminate these disadvantages there was designed, still for the employment in the winemaking field, a diaphragm press as disclosed in German Pat. No. 2,352,300. The role of the hose-shaped diaphragm was assumed by a diaphragm having a flat or planar surface. Such diaphragm was secured internally of the press container, which rotated about its horizontal axis, in a plane disposed transversely to the axis thereof. In particular, the diaphragm was secured, in the case of a short container, at the region of an end wall thereof and, when using a longer container, approximately at the longitudinal central region of the container. The arrangement was accomplished in this manner in order to avoid overstretching of the diaphragm, since the latter, as opposed to the hose-shaped diaphragm, had to be arched or domed not in a crosswise direction but in the direction of the lengthwise axis of the container. However, with a container wherein the diaphragm was attached at the longitudinal central region thereof, the entire volume of the container could only be used if the diaphragm, which in the unloaded or relieved state had a flat surface, was arched or domed back opposite to the pressing direction during the course of the filling-in of the mash. For this purpose it was necessary to evacuate the pressure compartment. This is a time-consuming and, in addition, expensive process, especially for large volume containers.
To overcome these drawbacks there was initially contemplated a modified design where in an elongate container there is provided a diaphragm not only at one end wall but also at the other end wall of such container, such as has been disclosed in Swiss Pat. No. 226,437. This arrangement was used in conjunction with a diaphragm press of the previously mentioned type, wherein, however, such diaphragm press was used as a laundry press. From the same Swiss Pat. No. 226,437 it becomes evident that the danger of overstretching the diaphragm does not even occur in an elongate container which rotates about its horizontal lengthwise axis, if the diaphragm is not arranged at an end wall but rather such that it bears against the container jacket or shell. Corresponding to the diameter thereof, the maximum deflection of the diaphragm is in any case smaller than if the diaphragm has to be deflected in the direction of the lengthwise container axis, especially if the length of the container amounts to a multiple of the diameter thereof.
These findings also has an influence upon the design of winemaking presses. In fact, the press according to Swiss Pat. No. 579,979, which was especially intended for fruit mash, was equipped with a diaphragm which was secured approximately in the plane of the rotational axis of the container. The diaphragm, which in the unloaded state has a substantially flat surface or bag-shaped configuration, only can be or needs to be domed in crosswise direction. Even with a flat surface of the diaphragm there does not exist any danger of overstretching. If the diaphragm has a substantially bag-shaped configuration, as described above in conjunction with U.S. Pat. No. 2,538,403, such danger does not exist in the first place. However, even with this construction of diaphragm there arises exactly the problem which was intended to be avoided by means of a substantially hose- or tubular-shaped diaphragm. Especially with large capacity containers the outlet paths through the mash to the drainage channels, which are arranged at the wall opposite the diaphragm, are far too long. Moreover, the permeability of the material to be pressed, of course, becomes increasingly smaller as the compaction thereof increases. Just as with the arrangement according to the aforementioned U.S. Pat. No. 2,538,403, the entire space of the press container can be better exploited when using a substantially bag-shaped diaphragm, but the yield in juice is specifically affected thereby.